【作者】 卫海桥；

【导师】 舒歌群；

【作者基本信息】 天津大学 ， 动力机械及工程， 2004， 博士

【摘要】 直喷式柴油机燃烧噪声对整机噪声的贡献是占主要地位的,而工况的瞬态变化首先反映的是内燃机工作过程的变化。因此,对内燃机在瞬态工况下噪声的剧烈变化现象的研究中,瞬态工况对内燃机燃烧噪声的影响机理是必须加以解决的问题。本文以直喷式柴油机作为研究对象,利用小波分析技术和相干分析技术研究内燃机缸内压力、表面振动与燃烧噪声的关系,确定活塞拍击噪声出现的主要频率在 4000Hz 和 7200Hz 附近。设计一种新的试验方法来测量燃烧激励谱与燃烧噪声谱,求取反映发动机结构衰减的燃烧噪声传递函数,开展燃烧噪声识别的研究工作,实现燃烧噪声与活塞拍击噪声的分离。从流体动力学角度建立缸内压力数学模型,研究缸内压力的频谱特性。通过缸内压力、缸内压力升高率及放热率与设计时间窗获取的燃烧噪声的分析,进行气体动力载荷与燃烧噪声的关系研究,结果表明压力升高率是影响燃烧噪声的主要的动力载荷因素。应用声响应法和 Sysnoise 声学软件进行模态试验和模态分析,研究燃烧噪声高频激励机理,发现燃烧室空腔声模态受空腔容积和温度的影响,进而影响着缸内压力高频振荡。通过有限元方法计算燃烧室空腔在点声源激励下的声压响应,确定了燃烧室空腔在激励力作用下产生较强烈的压力振荡的频率。通过对缸内压力和燃烧噪声各频带的能量分析,发现占燃烧压力总能量 5%左右的缸内压力高频振荡,激励的燃烧噪声能量占其总能量的 80%。研究表明,发动机的结构决定了燃烧噪声传递特性,燃烧噪声的主要成分集中在 800～4000Hz 频段,该频段的燃烧噪声是压力升高率和压力高频振荡共同作用的结果。开展内燃机瞬态工况测试技术和测试方法研究,揭示瞬态工况燃烧噪声激励机理。运用多元回归分析方法,建立动力载荷、压力高频振荡与燃烧噪声的一级影响模型。研究燃烧噪声二级影响因素对瞬态工况燃烧噪声影响关系。研究结果表明,瞬态工况壁面温度、喷油压力、针阀升程最大值和针阀开启持续时间均高于同负荷同转速的稳态工况,导致瞬态工况滞燃期、燃烧始点和喷油量与稳态工况相比产生差异,引起燃烧压力、压力升高率和高频压力振荡频率和幅值发生变化,使得瞬态工况与稳态工况燃烧噪声产生差异。更多还原

【Abstract】 The combustion noise plays an important role in the whole noise of DI dieselengine. As we know, the transient changing of conditions reflect the changing of thework process, in order to study the phenomena that the noise change acutely in thetransient conditions, it is necessary for us to result the effect mechanism of thetransient conditions on combustion noise. In this article, a single cylinder DI diesel engine is chosen as the research object,by using the wavelet packet analysis and coherence analysis methods to study therelationship between the cylinder pressure and surface vibration and the combustionnoise, the results show that the noise made by the piston slapping mainly presents atthe frequencies of 4000 hertz and 7200 hertz. In order to separate the noise of pistonslapping from the combustion noise and identify the combustion noise, a newexperiment method is designed to measure the spectrum of combustion stimulate andthe spectrum of the combustion noise, the transfer function of the combustion noisewhich reflects the structure attenuation of engine can be obtained. From the point of view of hydrokinetics the cylinder pressure mathematicmodel is established and its spectrum character is studied in detail. With the relationinvestigation of aerodynamic load and combustion noise through the analysis ofcylinder pressure, rate of pressure rise, heat release rate and combustion noiseobtained by design a time window, it is found that the rate of pressure rise is themain dynamic load factor that affects the combustion noise. By using the soundmodel experiment and model analysis with method of sound response and Sysnoisesound software, the high-frequency stimulation mechanism of combustion noise isstudied. With the influence of chamber volume and temperature on sound model ofcombustion chamber, it further affects the high-frequency oscillation of combustionpressure. With FEM analysis method the sound pressure response is calculatedwhen stimulation by a point sound source in the combustion chamber, and thefrequency of pressure oscillation rather violent is obtained when combustionchamber is stimulated by combustion. With the analysis of cylinder pressure andcombustion noise energy in each frequency range, it is found that thehigh-frequency oscillation pressure’s energy is only 5% of the total energy of the II<WP=5>combustion pressure; however, the combustion noise’s energy inspired by it is 80%of the whole combustion noise energy. The results show that the structure of theengine determines the transfer character of combustion noise. Combustion noise’smain component concentrates in the frequency range of 400~8000 Hertz and it isdetermined by the rate of pressure rise and high-frequency oscillation ofcombustion pressure working together. By developing testing technique and method of transient conditions, thestimulation mechanism in transient conditions of internal-combustion engine isstudied in detail. By using the method of multi-regression analysis, the first-levelinfluence model of dynamic load, high-frequency of pressure oscillation andcombustion noise can be established. The relation of second-level influence factorsof combustion noise in transient conditions is investigated too. It will result indifference of the ignition delay, start point of combustion, and fuel injectionquantity in transient conditions compared with steady condition, because thecombustion chamber wall’s temperature, fuel injection pressure, maximum ofneedle lift and unseal standing time of needle lift in transient conditions are higherthan steady conditions in the same load and rotation speed. As a result, it’ll causethe difference of combustion pressure, rate of pressure rise and oscillationfrequency and amplitude of high-frequency oscillation of combustion pressurebetween transient and steady conditions, and make difference with combustionnoise.更多还原